title: The human proteasomal subunit HsC8 induces ring formation of other alpha-type subunits.
abstract: The eukaryotic 20 S proteasome is a barrel-shaped protease complex, made up of four seven-membered rings. The outer and inner rings contain seven different alpha and beta-type subunits, respectively, each subunit located at a defined position. Recently, we have reported that the recombinant human alpha-type subunit C8 (HsC8) assembles into a heptameric ring-like structure by itself. In the present study we show that the two naturally neighboring alpha-type subunits of HsC8, HsPROS30 and HsPROS27, do not form ring-like complexes by themselves, but only dimers. This indicates that the propensity to form homo-oligomeric rings is not a general feature among human alpha-type subunits. However, coexpression of HsC8 and either of these neighbor alpha-type subunits results in the formation of hetero-oligomeric ring complexes, resembling the HsC8 ring-like structure. The ratio between the two types of subunits in the mixed complexes is surprisingly heterogeneous, varying from very high to very low HsC8 content. The three tested alpha-type subunits thus apparently lack binding sites that selectively interact with a specific neighboring subunit. This suggests that the correct positioning of the different alpha-type subunits in the eukaryotic 20 S proteasome is not dictated by the alpha-type subunits themselves, but rather by the interaction with specific beta-type subunits.
authors.affiliation: Department of Biochemistry, University of Nijmegen, The Netherlands.
authors.forename: W L
authors.initials: WL
authors.lastname: Gerards
authors.forename: W W
authors.initials: WW
authors.lastname: de Jong
authors.forename: H
authors.initials: H
authors.lastname: Bloemendal
authors.forename: W
authors.initials: W
authors.lastname: Boelens
mesh_terms: D003001:Cloning, Molecular; D003546:Cysteine Endopeptidases / Q000378:metabolism* / Q000502:physiology* / Q000648:ultrastructure; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005822:Genetic Vectors; D006801:Humans; D046911:Macromolecular Substances; D009097:Multienzyme Complexes / Q000378:metabolism* / Q000502:physiology* / Q000648:ultrastructure; D046988:Proteasome Endopeptidase Complex; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D011994:Recombinant Proteins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex